Polymer-based electroluminescent devices (PLEDs) have the potential for providing inexpensive alternatives to alpha-numeric displays and x-y addressable displays. PLEDs also have the potential to provide an alternative to back lighted, liquid crystal displays. A simple PLED may be constructed from an electroluminescent layer sandwiched between an electron injection electrode and a hole injection electrode. The electroluminescent layer is typically constructed by depositing a conjugated or conductive polymer on one of the electrodes. Devices based on poly(p-phenylenevinylene) (PPV), or derivatives thereof, have been demonstrated with sufficient quantum yields to be commercially attractive. More complicated devices utilize electron and hole transport layers between the above mentioned electrodes and the electroluminescent layer. The electroluminescent layer generates light when holes and electrons recombine in the layer.
The deposition and patterning of the electroluminescent layer present significant technical problems that must be overcome before economically attractive devices can be fabricated. If the conjugated polymer is soluble in a solvent, a thin film can be made by the spin-coating of a polymer solution. While spin-coated polymer films having good electro-optical properties can be obtained in this manner, the adhesion of spin-coated film to the underlying layer is often insufficient. In addition, many attractive polymers are not sufficiently soluble to be applied via spin-coating.
Spin-coating and other processes in which the entire substrate is coated, present additional problems in multi-color displays in which different "pixels" must be coated with different polymers. The deposition of each layer requires a three-step procedure consisting of a masking step to protect areas that are not to be coated, the spin-coating step, and a mask removal step. In addition to the increased complexity of the masking steps, the solvents utilized with conventional masking systems are often incompatible with the polymers being deposited. Accordingly, it would be advantageous to provide a system that does not require such masking operations.
Broadly, it is the object of the present invention to provide an improved method for depositing an electrically conducting or electroluminescent film.
It is another object of the present invention to provide a method that may be utilized with materials that cannot be spin-cast.
It is further object of the present invention to provide a method that can selectively deposit such films without the use of the masking operations discussed above.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.